Coaxial geothermal probe and method for making a coaxial geothermal probe

ABSTRACT

A method for making coaxial geothermal probes that comprise a hollow outer pipe ( 2 ) and an inner pipe ( 5 ), wherein inserting the outer pipe ( 2 ) in the ground comprises: —driving into the ground using pressure, applying an axial thrust to it that is generated by means of a hydraulic actuator ( 30 ), a head element ( 13 ) that is tubular and closed at the bottom by a driving head ( 18 ) and equipped with a first thread ( 19 ) at the top; screwing a second thread ( 24 ) of an additional tubular element ( 14 ) to the first thread ( 19 ) of the head element ( 13 ), creating a fluidtight connection between the head element ( 13 ) and the additional element ( 14 ); further driving into the ground ( 11 ) using pressure the assembly constituted of the head element ( 13 ) and of the additional element ( 14 ), applying an axial thrust to them that is generated by means of a hydraulic actuator ( 30 ); and optionally performing once or more the steps of screwing the second thread ( 24 ) of a further additional element ( 14 ) to a free first thread ( 19 ) of an additional element ( 14 ) already driven into the ground ( 11 ) and connected to the head element ( 13 ), and further driving the whole assembly into the ground ( 11 ) using pressure.

This invention relates to a coaxial geothermal probe and a method for making it.

It is known that one of the main components of geothermal heating plants is the so-called geothermal probe, which is just a pipe having an inlet and an outlet and which is intended to be inserted in the ground.

Of the various types of prior art geothermal probes, the coaxial type are constituted of two coaxial pipes that between them form an annular chamber and that are intended to be vertically installed in the ground. In particular, the outer pipe has a capped lower end, whilst the lower end of the inner pipe is at a slight distance from the lower end of the outer pipe, so that it is in fluid communication with the annular chamber. In use, the carrier fluid arriving from the heat pump is fed to the inner pipe, flows all the way through it, then returns towards the heat pump along the annular chamber, exchanging heat with the ground.

At present, the only known method for making coaxial geothermal probes comprises making a hole in the ground, inserting the outer pipe in it, filling any spaces between the outer pipe and the inner walls of the hole, and inserting the inner pipe in the outer pipe.

However, this prior art technology has several disadvantages, above all in economic terms. In fact, the need to make relatively long (usually around 100 to 200 metres) vertical boreholes means that the costs of making the probes is such that it renders the probes not economically viable, especially if the geothermal heating plant must be coupled with buildings that have low energy consumption.

In this context, the technical purpose which forms the basis of this invention is to provide a coaxial geothermal probe and a method for making it which overcome the above-mentioned disadvantages.

In particular, the technical purpose of this invention is to provide a coaxial geothermal probe and a method for making it which have production costs notably lower than the prior art probes.

The technical purpose specified and the aims indicated are substantially achieved by a coaxial geothermal probe and a method for making it, as described in the appended claims.

Further features and the advantages of this invention are more apparent in the detailed description, with reference to the accompanying drawings which illustrate several preferred, non-limiting embodiments of a coaxial geothermal probe and a method for making it, in which:

FIG. 1 is a schematic side view of a head element 13 that is part of an outer pipe of the probe according to this invention;

FIG. 2 is an axial section of the head element 13 of FIG. 1;

FIG. 3 is a schematic side view of a second element that is part of an outer pipe of the probe according to this invention;

FIG. 4 is an axial section of the second element of FIG. 3;

FIG. 5 is a schematic side view of a first step for making the probe according to this invention;

FIG. 6 is a schematic side view of a second step for making the probe according to this invention;

FIG. 7 is a schematic side view of a third step for making the probe according to this invention;

FIG. 8 is a schematic side view with some parts cut away of a fourth step for making the probe according to this invention;

FIG. 9 is an axial section of an example of an outer pipe of a probe made according to this invention;

FIG. 10 is an axial section of an example of a probe made according to this invention that comprises the outer pipe of FIG. 9 and that is connected to a geothermal plant;

FIG. 11 is an enlarged view of the detail XI of FIG. 9;

FIG. 12 is an enlarged view of the detail XII of FIG. 10; and

FIG. 13 is an enlarged view of the detail XIII of FIG. 10.

With reference to the above-mentioned figures, the numeral 1 denotes in its entirety a geothermal probe made according to this invention.

Similarly to prior art coaxial geothermal probes, those according to this invention comprise a hollow outer pipe 2 having a fluidtight closed first lower end 3 and an open first upper end 4, and an inner pipe 5 coaxial with the outer pipe 2 and advantageously made of a plastic material such as polyethylene. Between the inner pipe 5 and the outer pipe 2 there is an annular chamber 6, coaxial with the inner pipe 5 (annular in the sense that its cross-sections, relative to a longitudinal axis of the inner pipe 5 and of the outer pipe 2, have an annular shape, in particular the shape of a circular ring). The inner pipe 5 comprises a second lower end 7 that is placed near the first lower end 3 and that is in fluid communication with the annular chamber 6, and a second upper end 8 that is accessible near the first upper end 4.

In use, the first upper end 4 and the second upper end 8 are connected to the geothermal circuit 9 in such a way that the pump 10 sends the operating fluid to the inner pipe 5 and in such a way that the operating fluid exchanges heat with the ground 11 as it rises again along the annular chamber 6 and then is fed to the heat pump 12 of the plant again (FIG. 9).

According to this invention, the outer pipe 2 is preferably made of a metal material (advantageously steel) and comprises a head element 13 (FIGS. 1 and 2) and one or more additional elements 14 (FIGS. 3 and 4). The head element 13 is the element intended to constitute the first lower end 3 that in use is positioned at the maximum depth in the ground 11, whilst the one or more additional elements 14 are connected in series one after another as far as the surface of the ground 11.

In more detail, the head element 13 comprises a first straight tubular body 15 extending from a first end 16 to a second end 17, and a driving head 18 that seals in a liquidtight way the first end 16 to which it is connected. In contrast, the second end 17 is open and comprises at least one first thread 19. In the embodiment illustrated the first thread 19 is a female thread. Moreover, advantageously, the head element 13 comprises a first sealing band 20 that, in the embodiment illustrated, is constituted of a first cylindrical surface that is positioned adjacent to the first thread 19 on the side towards the driving head 18, and that is facing inwards.

The driving head 18 is advantageously tapered and at its free end comprises a more or less pointed tip.

Each additional element 14 comprises a second straight tubular body 21 that extends from a third end 22 to a fourth end 23. Both the third end 22 and the fourth end 23 are open. Moreover, also the fourth end 23 comprises a first thread 19 (identical to that of the second end 17) whilst the third end 22 comprises a second thread 24 that is screwed to the first thread 19 of the head element 13 or of a different additional element 14. In the embodiment illustrated, the second thread 24 is a male thread so that it can be coupled to the first, female thread 19, but the opposite solution may be freely adopted. Moreover, advantageously, the additional element 14 comprises a second sealing band 25 that, in the embodiment illustrated, is constituted of a second cylindrical surface that is adjacent to the second thread 24 on the side opposite that where the third end 22 is located, which faces outwards and is provided with suitable seats for one or more sealing O-rings 26 designed to be squeezed between the first sealing band 20 and the second sealing band 25 (FIG. 11). In this case too, it is possible to swap over the first sealing band 20 and the second sealing band 25.

Advantageously, the driving head 18 externally comprises at least one set of blades (solution not illustrated) or one helical thread 27 that, preferably, extend in a helix with a direction of screwing opposite to that of the second threads 24 of the third ends 22, in such a way that an axial rotation of the head element 13 corresponds both to a screwing movement of the driving head 18 into the ground 11 and a screwing movement of the first thread 19 of the head element 13 or of an additional element 14 connected to it, into a second thread 24 to which the first thread 19 may be connected.

Advantageously, the first tubular body 15 and the second tubular body 21 both have a circular cross-section and have the same maximum external radius (preferably constant), whilst the driving head 18 has a maximum radial projection relative to a longitudinal axis of the first tubular body 15, that is greater than the maximum external radius, so that the penetration of the head in the ground 11 creates a hole with a diameter greater than that of the tubular bodies 15, 21. In fact, in this way, as the various elements advance in the ground 11, the only resistance encountered is that of the ground 11 on which the driving head 18 acts. In contrast, when the driving head 18 has a maximum radial projection, relative to the longitudinal axis of the first tubular body 15, that is less than or equal to the maximum external radius, during advancing in the ground 11 the various tubular bodies 15, 21 laterally scrape on the ground 11, meaning that the friction generated by the ground 11 gradually increases as the outer pipe 2 is inserted in the ground 11.

As regards the method according to this invention, it should first be emphasised that since it is a method that allows the geothermal probes described above to be made, what is described with reference to the probe must also be considered valid for the method and vice versa.

Like all of the methods for making coaxial geothermal probes, even the method according to this invention comprises in general the operating steps of inserting in the ground 11 a hollow outer pipe 2 that comprises a fluidtight closed first lower end 3, and an open first upper end 4, and a step of inserting in the outer pipe 2 an inner pipe 5 that is coaxial with it, leaving between the two pipes an annular chamber 6 that is also coaxial with them. Advantageously, the inner pipe 5 comprises a second lower end 7 that is positioned near the first lower end 3 and in such a way that it is in fluid communication with the annular chamber 6. In contrast, a second upper end 8 of the inner pipe 5 is made accessible near the first upper end 4. Advantageously, the inner pipe 5 is made of plastic material such as polyethylene, and is inserted (manually or in another way) in the outer pipe 2 once the latter has been inserted in the ground 11.

According to this invention, the step of inserting the outer pipe 2 in the ground 11 comprises first the operating steps of preparing a head element 13 and one or more additional elements 14, preferably made of a metal material (advantageously steel). In particular, it comprises the head element 13 comprising a first straight tubular body 15 that extends from a first end 16 to a second end 17 which comprises a first thread 19, and a driving head 18 that seals the first end 16 in a liquidtight way, as well as each additional element 14 comprising a second straight tubular body 21 that extends from a third end 22 to a fourth end 23, the third end 22 and the fourth end 23 both being open. It also comprises also the fourth end 23 comprising a first thread 19 and the third end 22 comprising a second thread 24 that is screwable to the first thread 19 of the head element 13 or of a different additional element 14.

The method also comprises the operating step of driving the head element 13 into the ground 11 using pressure, starting with the driving head 18 and preferably in a vertical direction of insertion. In particular, this invention comprises that step of driving using pressure (like the others described below) being performed by applying to the head element 13 an axial thrust (that is to say, aligned with the longitudinal axis of the first tubular body 15) that is gradually generated by means of a hydraulic actuator 30 which is rested on the second end 17 or made to adhere to the first tubular body 15 and which is continuously fed with a pressurised operating fluid (oil) that guarantees the desired thrust.

The method then comprises screwing the second thread 24 of an additional element 14 to the first thread 19 of the head element 13, creating a fluidtight connection between the head element 13 and the additional element 14, and further driving into the ground 11 using pressure the assembly constituted of the head element 13 and of the additional element 14, in this case too applying an axial thrust to them that is generated by means of a hydraulic actuator 30.

Depending on requirements, that is to say, depending on the length of the geothermal probe 1 to be made, and the lengths of the head element 13 and of the additional elements 14 (the latter are preferably between 1 and 3 metres), the method may optionally comprise performing once or more the steps of screwing the second thread 24 of a further additional element 14 to the free first thread 19 of an additional element 14 already driven into the ground 11 and connected to the head element 13, and further driving into the ground 11 using pressure the assembly constituted of the head element 13 and the additional elements 14 connected to it by screwing, applying an axial thrust to them that is generated by means of a hydraulic actuator 30.

Although driving of the outer pipe 2 into the ground 11 may be performed by making it advance exclusively axially, in contrast, in the preferred embodiment during the various steps of driving using pressure, the head element 13 and any additional elements 14 are also made to rotate about their longitudinal axis. For that purpose it is advantageously possible to use a head element 13 equipped with a driving head 18 externally comprising at least one set of blades or one helical thread 27 of the type described above, and which is substantially screwed into the ground 11 as it advances.

Depending on the embodiments, it may alternatively be the case that the head element 13 and any additional elements 14 are made to rotate about their longitudinal axis by means of only the interaction between the set of blades or the helical thread 27 of the driving head 18 and the ground 11, under the action of the axial thrust acting on them (in others the set of blades or the helical thread 27 are shaped in such a way that an axial thrust applied to the head element 13 causes its automatic screwing into the ground 11), or that the head element 13 and any additional elements 14 are made to rotate about their longitudinal axis in an active way by means of a specific actuator, for example acting on the tubular body of the element accessible outside the ground 11.

As already indicated, if the driving head 18 has a maximum radial projection relative to a longitudinal axis of the first tubular body 15, that is greater than the maximum external radius, the penetration of the head in the ground 11 creates a hole with a diameter greater than that of the tubular bodies. Moreover, in this case the method comprises, once all of the steps of driving using pressure are complete, a step not illustrated of filling any empty spaces 28 present between the ground 11 and the various tubular bodies present (first tubular body 15 and one or more second tubular bodies).

From the above description, it seems clear that the method for making the probe according to this invention may be implemented in any ground 11 in which there are no rock formations present, that is to say, in any ground 11 in which probe driving is possible without drilling.

This invention brings important advantages.

In fact, thanks to this invention, it has been possible to provide a coaxial geothermal probe and a method for making it, which have production costs notably lower than for prior art probes. In fact, probe installation no longer requires expensive deep drilling to be carried out. It is sufficient to have available a device capable of driving using pressure.

It should also be noticed that thanks to this invention it is also possible to use a notably different approach in the design of geothermal probes, replacing traditional very deep probes (more than 100 metres) with a larger number of shorter probes, without substantially increasing the costs, since it is no longer necessary to carry out expensive preliminary drilling operations. Moreover, thanks to this advantage, it is also possible to use the technology disclosed in types of ground that have rocky inclusions located at a depth of several dozen metres, by making a plurality of relatively short probes instead of one relatively long probe.

Finally, it should be noticed that this invention is relatively easy to produce and that even the cost linked to implementing the invention is not very high. The invention described above may be modified and adapted in several ways without thereby departing from the scope of the inventive concept.

All details may be substituted with other technically equivalent elements and the materials used, as well as the shapes and dimensions of the various components, may vary according to requirements. 

1. A method for making coaxial geothermal probes, comprising the operating steps of: inserting in the ground (11) a hollow outer pipe (2) comprising a first lower end (3) that is sealed in fluidtight way, and a first upper end (4) that is open; inserting in the outer pipe (2) an inner pipe (5) coaxial with it, forming an annular chamber (6) coaxial with the inner pipe (5) and located between the inner pipe (5) and the outer pipe (2); the inner pipe (5) comprising a second lower end (7) that is positioned near the first lower end (3) and is in fluid communication with the annular chamber (6) and a second upper end (8) that is accessible near the first upper end (4); wherein the step of inserting the outer pipe (2) in the ground (11) comprises the operating steps of: preparing a head element (13) comprising a first straight tubular body (15) extending from a first end (16) to a second end (17), and a driving head (18) that seals the first end (16) in a liquidtight way, the second end (17) comprising a first thread (19); starting with the driving head (18), driving the head element (13) into the ground (11) using pressure, applying an axial thrust to it that is generated by means of a hydraulic actuator (30); preparing one or more additional elements (14) each comprising a second straight tubular body (21) extending from a third end (22) to a fourth end (23), the third end (22) and the fourth end (23) both being open, also the fourth end (23) comprising a first thread (19) and the third end (22) comprising a second thread (24) that can be screwed to the first thread (19) of the head element (13) or of a different additional element (14); screwing the second thread (24) of an additional element (14) to the first thread (19) of the head element (13), creating a fluidtight connection between the head element (13) and the additional element (14); further driving into the ground (11) using pressure the assembly constituted of the head element (13) and of the additional element (14), applying an axial thrust to them that is generated by means of a hydraulic actuator (30); optionally performing once or more the steps of screwing the second thread (24) of a further additional element (14) to the free first thread (19) of an additional element (14) already driven into the ground (11) and connected to the head element (13), and further driving into the ground (11) using pressure the assembly constituted of the head element (13) and the additional elements (14) connected to it by screwing, applying an axial thrust to them that is generated by means of a hydraulic actuator (30).
 2. The method according to claim 1, wherein during the steps of driving using pressure, the head element (13) and any additional elements (14) are also made to rotate about their longitudinal axis.
 3. The method according to claim 2, wherein a head element (13) is used that is equipped with a driving head (18) externally comprising at least one set of blades or one helical thread (27).
 4. The method according to claim 3, wherein a head element (13) is used in which the set of blades or the helical thread (27) extend in such a way that their screwing into the ground (11) occurs with a direction that can cause screwing of each first thread (19) to a second thread (24) that may be coupled to it.
 5. The method according to claim 3, wherein the head element (13) and any additional elements (14) are also made to rotate about their longitudinal axis by means of the interaction between the set of blades or the helical thread (27) of the driving head (18) and the ground (11) under the action of the axial thrust acting on them.
 6. The method according to claim 2, wherein the head element (13) and any additional elements (14) are also actively made to rotate about their longitudinal axis by means of a specific actuator.
 7. The method according to claim 1, also comprising after all of the steps of driving using pressure, a step of filling any empty spaces present between the ground (11) and the first tubular body (15) and the one or more second tubular bodies.
 8. A coaxial geothermal probe, comprising: a hollow outer pipe (2) comprising a first lower end (3) that is sealed in fluidtight way and a first upper end (4) that is open; and an inner pipe (5) coaxial with the outer pipe (2), an annular chamber (6), coaxial with the inner pipe (5), being present between the inner pipe (5) and the outer pipe (2); the inner pipe (5) comprising a second lower end (7) that is positioned near the first lower end (3) and is in fluid communication with the annular chamber (6), and a second upper end (8) that is accessible near the first upper end (4); wherein the outer pipe (2) comprises: a head element (13) in turn comprising a first straight tubular body (15) extending from a first end (16) to a second end (17), and a driving head (18) that seals the first end (16) in a liquidtight way, the second end (17) being open and comprising a first thread (19); one or more additional elements (14) each comprising a second straight tubular body (21) extending from a third end (22) to a fourth end (23), the third end (22) and the fourth end (23) both being open, the fourth end (23) also comprising a first thread (19) and the third end (22) comprising a second thread (24) screwed to the first thread (19) of the head element (13) or of a different additional element (14); and wherein the driving head (18) externally comprises at least one set of blades or one helical thread (27).
 9. (canceled)
 10. The geothermal probe according to claim 8, wherein the set of blades or the helical thread (27) extend in a helix with a direction of screwing opposite to that of the second threads (24) of the third ends (22).
 11. The geothermal probe according to claim 8, wherein the first thread (19) has a female shape and the second thread (24) has a male shape.
 12. (canceled)
 13. The geothermal probe according to claim 10, wherein the first thread (19) has a female shape and the second thread (24) has a male shape.
 14. The geothermal probe according to claim 10, wherein the first tubular body (15) and the second tubular body (21) have a circular cross-section and have the same maximum external radius, and wherein the driving head (18) has a maximum radial projection relative to a longitudinal axis of the first tubular body (15) that is greater than the maximum external radius.
 15. The method according to claim 4, wherein the head element (13) and any additional elements (14) are also made to rotate about their longitudinal axis by means of the interaction between the set of blades or the helical thread (27) of the driving head (18) and the ground (11) under the action of the axial thrust acting on them.
 16. The method according to claim 3, wherein the head element (13) and any additional elements (14) are also actively made to rotate about their longitudinal axis by means of a specific actuator.
 17. The method according to claim 4, wherein the head element (13) and any additional elements (14) are also actively made to rotate about their longitudinal axis by means of a specific actuator.
 18. The method according to claim 2, also comprising after all of the steps of driving using pressure, a step of filling any empty spaces present between the ground (11) and the first tubular body (15) and the one or more second tubular bodies.
 19. The method according to claim 3, also comprising after all of the steps of driving using pressure, a step of filling any empty spaces present between the ground (11) and the first tubular body (15) and the one or more second tubular bodies.
 20. The method according to claim 5, also comprising after all of the steps of driving using pressure, a step of filling any empty spaces present between the ground (11) and the first tubular body (15) and the one or more second tubular bodies.
 21. The method according to claim 6, also comprising after all of the steps of driving using pressure, a step of filling any empty spaces present between the ground (11) and the first tubular body (15) and the one or more second tubular bodies.
 22. The geothermal probe according to claim 8, wherein the first tubular body (15) and the second tubular body (21) have a circular cross-section and have the same maximum external radius, and wherein the driving head (18) has a maximum radial projection relative to a longitudinal axis of the first tubular body (15) that is greater than the maximum external radius. 